There are various water separators in use today that are specifically utilized in medical applications where a sample of the patient's exhalation is desired for analysis of the various constituents in such exhaled gases. Such water separators are necessary since the exhaled gases contain liquids from the patient and such liquids must be removed or in some way isolated so that only dry gas is seen by the gas analyzer.
Typical of such water separators are disclosed in U.S. Pat. No. 4,558,708 of Aida et al.; U.S. Pat. No. 4,558,709 of Labuda et al.; U.S. Pat. No. 4,600,412 of Liston et al.; U.S. Pat. No. 4,446,869 of Knodle and U.S. Pat. No. 4,382,806 of Hakala et al.
Such prior art separators employ various means of removing the liquid including filters, centrifuging, liquid sumps and the like, however, each type has various drawbacks in actual use.
The use of filters produces a separator susceptible to clogging and the inability to handle streams that, at times, may be 100% liquid. Dealing with exhaled gases from a patient, in which the gases may contain highly viscous liquids (such as mucous and saliva), is particularly difficult due to plugging of lines and/or filters by said liquids. Also, the passageways used to handle sampling of exhaled gases are small so as to take only a minute sample from the patient circuit. In addition, filters require constant attention for replacement, cleaning or disposal.
In the filter means of Labuda et al., for example, a hydrophobic baffle is directly in the patient circuit adjacent the mouthpiece and the main flow therethrough is bidirectional, that is, the flow reverses direction as the patient inhales and exhales. There is no means to continually draw that main stream through the baffle and thus, the baffle collects the liquid materials and needs to be constantly monitored and replaced since it is obviously not desirable to draw that liquid through the patient circuit to enter the patients airway or mask.
Centrifuges require of course, moving parts and thus are costly and relatively difficult to manufacture.
Liquid sumps generally pass the liquid/gas through a large reservoir where the liquid is drawn off the bottom and the dry air removed from the top of the reservoir. Such devices have fairly large dead air space and thus, the constituents in previous exhalations admitted to the reservoirs can affect the accuracy. Also, dead air space affects the wave form to the constituent monitors by increasing the response time, thus modifying the actual wave form.